Paper cassettes are used in electrophotographic copiers to store a supply of copy sheets. The cassettes are usually provided with a plate which normally rests on the bottom of the cassette, and upon which the supply of copy sheets is placed. As the supply is depleted, the plate must be raised so that the uppermost copy sheet remains in engagement with the paper feed roller assembly used to remove the sheets from the cassette.
In one type of cassette plate lifting mechanism, a roller is urged upwardly through an opening in the bottom of the cassette and into engagement with the underside of the plate to move the paper supply into engagement with the feed roller. The plate-lifting roller is mounted on an arm carried by a spring-loaded pivot shaft. Means is provided to disengage the loading spring to facilitate insertion and removal of the cassette. Mechanisms of this type either require a manual operation to disable the loading spring or the arrangement must permit the cassette to be moved in and out against the action of the loading spring.
While such arrangements keep the top sheet in engagement with the feed roller, the amount of force used cannot be controlled and varies with the amount of paper in the cassette. This requires the use of an immovable feed roller assembly, the rollers of which must overcome the spring force to remove the copy sheets from the cassette.
One example of a cassette arrangement of the type described is shown in U.S. Pat. No. 3,977,666.